In isolating substances present in cells of microorganisms, e.g., in preparing concentrates of food-purpose protein, enzyme preparations and the like it is necessary to break down cell membranes. For that purpose, there are apparatus in which cell membranes are destructed by mechanical, chemical or fermentation methods.
Among the apparatus using the mechanical methods of disintegration of cells are known extrusion apparatus, ballistical disintegrators and apparatus using the effect of decompression, wherein the cells are destructed on the account of expansion of gas dissolved in the cells under pressure upon an abrupt pressure decrease in suspension. The invention relates to the latter type of apparatus.
Prior are apparatus for decompression disintegration consist of two basic units. The first unit comprises one or two high-pressure vessels having pipelines for feeding thereto a cell suspension and a working gas (nitrogen, air, carbon dioxide and the like) under pressure for saturating the suspension. The vessels can have a suspension level regulator and stirring devices. The second basic unit is a disintegration device which comprises a specially designed valve ensuring an abrupt pressure decrease in the flow of the cell suspension.
The prior art apparatus for decompression disintegration of cells of microorganisms differ from one another mainly in the construction of the disintegration device.
In one embodiment, the disintegration device comprises a construction consisting of a top flange casing and a bottom flange casing which are vertically movable and have disk seats installed therein, the disk seat of the bottom casing having an annular projection defining with the outer surface of the top seat a working aperture, and the top casing has a passage for admitting the suspension to the working aperture (cf. USSR Inventor's Certificate No. 602550, Int. Cl. C 12 K 1/10).
In another embodiment a similar construction of the disintegration device is used, which differs in that the seat of the bottom casing has an additional annular projection and a passage for the removal of the suspension of disintegrated cells, the disk seat of the top casing having a number of grooves communicating with the passage admitting the suspension for distributing the suspension into the working aperture; in addition, an agitator is provided on the top casing for cleaning the working aperture upon clogging (cf. USSR Inventor's Certificate No. 602551, Int. Cl. C 12 K 1/10).
The abovedescribed apparatus for decompression disintegration function in the following manner. A cell suspension and a compressed gas are continuously fed to a mixing vessel having a float-type level gauge. When the suspension level in the mixing vessel increases, the level gauge opens the admission of compressed gas thereto, the gas bubbling under pressure through the suspension layer. Further, the suspension saturated with the gas passes through a receiver and is admitted to the disintegration device.
In the disintegration device the suspension is fed to the disk seat of the top casing and is then throttled through the aperture defined between the outer surface of the top seat and the annular projection (or projections) of the bottom seat to pass to the zone of normal pressure. The cells are thus disintegrated under the action of a decompression. The working pressure in the disintegration device is set-up by tightening adjusting screws and is measured by means of a pressure gauge.
The apparatus for decompression disintegration are characterized by a high enough efficiency of breaking of the cell membranes with metal mass and energy consumption which are much lower than in apparatus of other types. The apparatus function at a comparatively low working pressure (between 80 and 200 atm.g.). The decompression method used in such apparatus makes it possible to scale-up such apparatus to the capacity required in the commercial production.
The abovedescribed apparatus are, however, deficient in a complicated construction of the disintegration device and the need in manual adjustment of pressure in the disintegration device during operation.
An apparatus for continuously disintegrating cells of microorganisms disclosed in USSR Inventor's Certificate No. 492118, Int. Cl. C 12 1/10 comprises a mixing vessel for allowing a suspension of microorganisms to stay under pressure, a pipeline of a disintegration device connected thereto and to an accumulating vessel for disintegrated material. Pipelines connected to a compressed gas source and to a metering pump for supplying the suspension are connected to the mixing vessel containing the suspension. The apparatus has an automatic valve for maintaining a pre-set pressure in the vessel.
The disintegration device comprises two casings connected in series to one another and defining a supply chamber and a working chamber. The supply chamber has an inlet passage for feeding the compressed gas and an outlet chamber for pressure decrease, and the working chamber has a lateral inlet passage for admitting the suspension of cells; the chambers are separated by a membrane to which is secured a valve member installed in the working chamber. The casing of the working chamber is connected in series with an adjusting flange body and a needle seat body, the needle bearing with its working end against the seat, so that the seat aperture is closed on the side of the high pressure zone.
The apparatus functions in the following manner. A working pressure in the supply chamber of the disintegration device is built-up by the compressed gas. Subsequently the suspension of cells is fed to the mixing vessel by the metering pump. When the pre-set working pressure (about 100 atm.g.) is achieved, the compressed gas is admitted to the vessel, and the suspension saturated with the gas is discharged through the distintegration device into the accumulating vessel.
In the initial position, when the compressed gas is admitted to the supply chamber of the disintegration device, the outlet from the working chamber is shut-off by the needle valve which bears against the needle seat. When the pressure in the working chamber becomes greater than that in the supply chamber as a result of operation of the metering pump, the membrane separating the chambers is caused to move upward together with the needle valve secured thereto, and an aperture is defined between the shut-off end of the needle and its seat so that the suspension is decompressed through this aperture into the accumulating vessel. This results in the cells being disintegrated owing to the decompression.
The uniformity of decompression of the cell suspension is ensured by means of the adjusting flange which is bolted to the casing of the working chamber of the disintegration device.
The apparatus functions continuously and enables the degree of disintegration of cells of microorganisms at a rate of 70-75%.
It should be, however, noted that the arrangement of the needle valve inside the working chamber and the lateral admission of the suspension to the working chamber in the abovedescribed apparatus result in swirling of the suspension flow in the passage defined between the working chamber walls and the needle and also in swirling of the suspension jet discharged through the aperture defined by the needle and its seat. As a result, the time of pressure decrease in the suspension increases thus lowering the efficiency of disintegration. In addition, the movement of the suspension jet at the outlet from the disintegration device determined by the shape of the aperture between the needle and its seat is directed toward the needle axis thus impairing the atomization of the suspension, hence, lowering the efficiency of disintegration.
The construction of the disintegration device consisting of four series-connected elements--the supply chamber, the working chamber, the adjusting flange and the needle seat--is difficult to adjust upon a change in the operating conditions and replacement of various components, thus making the apparatus as a whole more complicated in structure.
In extrusion disintegration apparatus the cells are disintegrated by throttling the cell suspension from a high-pressure zone through a microaperture of a disintegration valve into a normal pressure zone. One of the most popular apparatus of this type is a hydraulic extruder manufactured by the U.S. Company Gaulin (cf. Rees, L. H., Chem. Engineering, 1974, 5, 13, 87). The apparatus structurally consists of two basic units: a high-capacity plunger pump and a spring-biased cuneiform disintegrating valve which is connected to the pump discharge. Both units are installed on a cast iron bed, together with a motor. The hydraulic pressure at the disintegration valve is adjusted either manually, by means of a handwheel, or remotely. The apparatus is designed for operation under recirculation of the cell suspension.
In operation a suspension of microorganisms is continuously admitted at a high pressure (between 250 and 700 atm.g.) to the interior of the valve, at a low velocity. The suspension then gets into a microaperture between the valve and its seat where the velocity rapidly increases, depending on the working pressure, and the suspension is throttled into the normal pressure zone where the cells of microorganisms are disintegrated to the extent determined by the value of the hydrostatic pressure, its gradient and rate of change, cavitation and turbulization effects. The residence time of the cell suspension within the microaperture about 1 .mu.m wide is 10.sup.-6 s.
The process of destruction of cells in the extrusion homogeneization apparatus features high working pressure (250-700 atm.g.), and the working cycle is to be repeated many a time for achieving high degree of cell disintegration (80-90%) so that fragments of cells of different size are obtained, and the separation of the solid and liquid phases of the resultant suspension becomes very difficult.